Genesis and distribution characteristics of natural gas in Dongpu Depression,Bohai Bay Basin
In view of the complex genesis of natural gas in the high thermal evolution area of Dongpu Depression and the unclear understanding of natural gas enrichment law and exploration potential,the genetic types and distribution characteristics of natural gas were studied by using cluster analysis and hydrocarbon generation simulation experiment.The results of research show that there are three main types of natural gas in Dongpu Depression:oil type gas,coal-derived gas and mixed gas,among which oil type gas includes low-maturity oil type gas(Ro is between 0.5％and 1.2％),midium-maturity oil type gas(Ro is between 1.2％and 1.6％)and high-maturity oil type gas(Ro is between 1.6％and 2.0％),successively distributing on the top of structure,slope belt and depression zone.Coal-derived gas Ro is between 2.0％and 3.0％,including high-maturity coal-derived gas both outside and inside the source.Mixed gas mainly distributes around major fractures surrounding source kitchen with high thermal evolution.Analysis on main gas generation area shows main gas generation depth of source rock corresponding to oil type gas and coal-derived gas is 4,000-5,000 and 5,000-7,000 m,which is spatially successive.Enrichment degree of natural gas is closely related to thermal evolution degree of hydrocarbon generation sag in Dongpu Depression.Mid and high thermal evolution sags(Ro is between 1.0％and 3.0％)are key fields for future gas exploration in Bohai Bay Basin and Dongpu Depression.
oil type gascoal-derived gasmain gas generation areanatural gas enrichmentDongpu DepressionBohai Bay Basin
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